package LeetCode._03_链表;

public class _06反转链表 {
    public class ListNode {
        int val;
        ListNode next;
        ListNode() {}
        ListNode(int val) { this.val = val; }
        ListNode(int val, ListNode next) { this.val = val; this.next = next; }
    }

    public ListNode reverseList(ListNode head) {
        if(head == null || head.next == null) return head;
        ListNode newHead = reverseList(head.next);
        head.next.next = head;
        head.next = null;
        return newHead;
    }

    public ListNode reverseList2(ListNode head) {
        if(head == null || head.next == null) return head;
        ListNode newHead = null;
        ListNode tmp = null;
        while(head!=null){
            tmp = head.next;
            head.next = newHead;
            newHead = head;
            head = tmp;
        }
        return newHead;
    }
}
